But physical outcomes worse versus full-term infants

Action Points

Note that this Florida population-based study found an association between birth at 41 weeks gestation and subsequent standardized test performance at ages 8-15.

Be aware that gestation lengths were based on birth certificate data, which may be biased in situations where conception can not be adequately dated.

Infants born beyond 40 weeks ("late-term") were linked to both higher test scores and a decreased risk of poor cognitive outcomes as school-age children, compared with their full-term (39-40 week) counterparts, a large retrospective study of Florida children found.

Overall, children born as late-term infants were associated with a statistically significantly higher score on standardized tests at age 8-15 (0.7% of a standard deviation, 95% CI 0.1%-1.3%, P=0.02) versus children born as full-term infants, reported David N. Figlio, PhD, of Northwestern University in Chicago, and colleagues.

Children in the late-term group were 3.1% less likely to have poor cognitive outcomes (95% CI 0.0%-6.1%, P=0.05). Compared with children in the full-term group, they were also 2.8% more likely to be considered "gifted" (95% CI 0.4%-5.2%, P=0.02), the authors wrote in JAMA Pediatrics.

"While modest in magnitude, these differences are not trivial," they asserted.

However, while cognitive outcomes for the late-term group may have been higher for the late-term group, the same could not be said for physical outcomes. In fact, the late-term group were 6% more likely to have "abnormal conditions" (P<0.001) and 2.1% more likely to be disabled than the full-term group, although the latter difference did not reach significance (P=0.08).

"One week extra development in utero certainly will lead to some differences at or near birth, but I find it hard to believe that any intelligence signal wouldn't simply be washed away amid all the other factors that affect developing young minds prior to age 8," he said.

He added that there was the potential for "systematic measurement error," as the gestational age came from birth certificate data, as well as unmeasured confounders that might lead to better outcomes (such as maternal nutrition).

Figlio and colleagues note that their findings provide "no useful course of action" for clinicians, but rather information for parents with uncomplicated, low-risk pregnancies and physicians who are deciding between induced labor at 39-40 weeks or expectant management beyond 40 weeks. They suggest a "tradeoff" for late-term infants between poorer health at birth and improved cognitive development as children.

"Because fetal maturation continues between full term and late term ... children born late term may subsequently demonstrate higher cognitive functioning, even if they initially face greater risks of health complications during the perinatal period," they wrote.

But because pregnancies that are expectantly managed are often high-risk, Figlio's team sought to control for that as well. They performed a separate analysis that excluded all infants with congenital anomalies, all pregnancies with labor or delivery complications, as well as pregnancies where the mother was older (>35 years). However, the results for the three main outcomes (test scores, poor cognitive outcomes and "gifted") remained similar.

When the authors limited their analysis further to only "low-risk, uncomplicated pregnancies" (excluding high-risk and labor and delivery complications, and only including women who spoke English or Spanish and had prenatal care in the first trimester), the risks of poorer outcomes decreased for the late-term group. The late-term group was 4% less likely to have poor cognitive outcomes, but the difference was no longer significant (P=0.12) and there was no longer an increase in abnormal conditions (0.5%, P=0.90).

The authors linked Florida birth certificate data to Florida Comprehensive Assessment Test scores for children ages 8-15 years. Of the 1,536,482 children examined, 51.2% were male, 22.1% of mothers were black and the mean age of mothers was 27.2 years. "Gifted" children were defined as having superior intellectual development and capable of high performance, while "poor cognitive outcomes" were defined as scoring in the fifth percentile of test-takers or having a disability that exempted the student from taking the test.

Figlio and colleagues acknowledge these limitations, and add that they also did not know which births were induced or performed cesarean sections, which further limits the study's generalizability.

This article was supported by grants from the National Science Foundation, the U.S. Department of Education, the Smith Richardson Foundation, and the Bill and Melinda Gates Foundation through the National Center for the Analysis of Longitudinal Data in Education Research.

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